This is probably a silly question, but it's something that I don't recall seeing covered in any of the writings on the subject (perhaps the authors assumed that it was so obvious as to not require explanation).
We all know that the AEC Regal was the single-deck version of the double-deck Regent, and that similarly the Leyland Tiger was the single-deck version of the double-deck Titan; but what exactly were the physical differences between the single- and double-deck chassis? On a front-engined vehicle, exactly what was it that made the chassis specifically single or double-deck?
Michael Wadman
26/01/13 - 11:44
When you read of operators rebodying Tigers as double deckers it was usually the case that new chassis rails were incorporated albeit using the running gear and perhaps some chassis components like cross members etc.
Andrew Charles
26/01/13 - 15:40
Looking at this question from the other end, what happened with a rear engine double deck chassis when fitted with a single deck body? Birmingham had single deck Fleetlines, for example, and Portsmouth had single deck Atlanteans, but they were built like that. Some people, and my experience is of Southampton, had some Atlantean double deckers rebodied in about 1990 with single deck bodies.
With Southampton, the old body was scrapped, the chassis was overhauled - to include updating the lubrication system - and shuffled up to Blackburn for new East Lancs bodies. They were known [and labelled] as Atlantean Sprints. The engine was not derated, and I don't think the suspension was softened to take account of the lighter body, so they were rather lively.
There were supposed to be ten of them, but the project ended after five. I have photographs of six of them, but that's another matter!
Pete Davies
27/01/13 - 08:02
Michael
Looking simply at the chassis versions you mention, in the immediate post-war period the fundamental difference was the wheelbase. Both PS1 and Regal had a 17'6" wheelbase to suit the maximum 27'6" body length, whereas the PD1 and Regent II with an overall length of 26' had 16'3" wheelbase. The other principal difference was the arrangement of the chassis at the rear end, with the need to provide a dropped frame or cantilevered members for the platform on a standard double-decker. The chassis members for the single deckers were probably of slightly smaller dimensions, and the other likely difference would have been between 9x20 wheels on the front axle for the single-deckers compared with 10x20 for double deckers.
As vehicle dimension limits were relaxed, the wheelbases also extended, but there was still a difference between single- and double-deck chassis.
Alan Murray-Rust
27/01/13 - 08:04
The principal difference between buses like the AEC Regal/Regent and Leyland Tiger/Titan was that single deckers had a longer wheel base than double deckers. The overall permitted length was also greater for a single decker so the chassis frame would be longer than that for a double decker.The road springs would also be stronger for a double decker to cope with the additional weight.
When SMT rebodied Tiger TS7s as double deckers during the War, new chassis side frames of TD4 specification were used, with the mechanical units from the Tiger being used in the new chassis frame.
Trent Motor Traction on the other hand had some Daimler COG5-40 single deckers rebodied as double deckers during the War and these retained their original chassis and had a compact 'rear end' as the original wheelbase was retained but the overall length of the vehicle could only be 26 feet as opposed to the 27 feet 6 inches allowed for single deckers.
When the overall length of double deckers was increased to 27 feet from 1950 and the 30 feet from 1956 rebodying front engined single deckers as double deckers became easier. Barton Transport, for example, had a number of Tiger PS1s rebodied as double deckers during 1957/58 by Willowbrook and NCME by upgrading the road springs to accommodate the heavier double deck bodies. The PS1's overall length of 27 feet 6 inches was not a problem as double deckers could now be up to 30 feet long.
Michael Elliott
29/01/13 - 06:41
Certainly not a silly question! One pair with similar-sounding names but some striking differences is Dennis's 1940s-1950s Lancet and Lance. The Lancet single-decker has Dennis's own axles, the radiator slightly offset to the nearside and a driving position where you sit with legs stretched out almost horizontally, so that your feet push the pedals forward rather than down. The Lance has Kirkstall axles, a different radiator--at least the shell is different--mounted centrally, and the pedals are set much lower than on the single-decker. The unique 5-speed gearbox is common to both, though I've a feeling that the decker was offered with a 4-speed option. Lance engine options were Gardner 6LW for the K2, Dennis O6 for the K3 and Gardner 5LW for the K4. The great majority of postwar Lancets had the O6. There were also the usual chassis member differences. At least one very sturdy-looking coach was built on a Lance chassis. I can't think of any other s-d/d-d pair where the difference was so marked. Corrections and additions to these notes greatly welcomed!
Ian Thompson
29/01/13 - 17:48
While I understand the various re-bodying issues which relate to the specific requirements of the wheelbase and overall lengths of both single and double deck chassis, are there many instances where the chassis was also modified so that the chassis could take a new 8' wide body where previously the chassis had carried a body which was only 7'6" wide?
Andrew Beever
03/02/13 - 11:27
Many thanks to all who have replied. It would appear then, that, apart from dimensions that obviously changed with legislation, the main differences were that the double-deck chassis would have more substantial chassis members, higher-rated springs, and support for the platform at the rear.
Michael Wadman
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